Batch process of edge plating aluminum ribbon with material that is readily soldered to other materials



Oct. 30, 1962 B. c. KARNER ETAL BATCH PBocEss oF EDGE PLATING ALUMINUM RIBBON WITH MATERIAL THAT IS READILY SOLDERED TO OTHER MATERIALS Filed May 19, 1960 INVENTORJ en/mko C. Kam/m Bfoefnr J. Aimar tats The present invention relates to the art of plating, and more particularly to the plating of the side edges of a roll of aluminum strip or ribbon material with a metallic material to which other metals can inexpensively be soldered.

This is a continuation-in-part of our previously tiled application, Serial No. 675,582, led August 1, 1957, and now abandoned.

Aluminum ribbon material is used extensively in the heat transfer field as fin material for heat transfer coils. In the conventional process, a continuous length of aluminum ribbon is helically wound on copper tubing in standard lin winding machines to form upstanding, spaced heat transfer tins on the tubes. Such tubes, with the aluminum fins provided thereon, become heat transfer coils and are lused in refrigerating and heating apparatus, the heat transfer taking place between fluid flowing through the tube and the ambient atmosphere which surrounds the tube and ns.

ln the usual process, the aluminum iins are tightly wound on the copper tubing to provide a good mechanical connection. However, it has been found that such a mechanical connection is not satisfactory when it is desired to increase the heat transfer ability of the coils. lt has been thought desirable to solder the aluminum ns to the tubes rather than to use a mechanical connection. Soldering of the aluminum fins to the tubes has the following advantages:

(a) A tight permanent joint between the fins and the tube is provided which improves the durability of the structure and permits greater latitude in designing such coils;

(b) A higher heat transfer rate results because the air gap resistance between the tins and the tube is eliminated;

(c) A higher heat transfer rate also results because the solder llets at the base of the fins increase the iin contact area and simulate the tapered iin-shape which is considered ideal for heat transfer; and

(d) A cost reduction is accomplished because thinner ns may be used to transfer as much heat as unsoldered thick ns.

Difficulties were encountered when it was attempted to solder pure aluminum to copper tubing. In order to effectuate such a solder, it is necessary to use expensive solder material containing a flux and also to use expensive soldering techniques. Alternately, the use of plated aluminum to permit soft soldering has been considered. However, the usual plating techniques are expensive and relatively impractical for plating the thin ribbon material utilized to fabricate heat transfer fins. For example, in order to keep the plating cost Within limits, it must be a continuous process. However, plating the aluminum ribbon in a continuous process would require a length of approximately 1500 feet of ribbon to be submerged in electro-plating tanks. This would mean that the plating apparatus would occupy an unreasonable amount of space in the plating plant. In addition, such a length of ribbon material would frequently snap and break, making a continuous process impractical. According to the concept of the present invention, these plating problems are overcome by plating an entire roll of aluminum ribbon,

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,A 3,961,527 Patented Oct. 30, 1962 mit the roll being formed of tightly wound convolutions to provide a unit in the shape of a flat disc. Plating such a disc provides the desired readily solderable material at the side edges of the aluminum ribbon, which is the only area necessary to permit soldering of the ribbon to a tube. In addition, great lengths of the ribbon may be contained in one roll, thus providing an economical plat ing process.

An object of the invention is to provide simple and inexpensive means for plating a readily solderable material onto the side edges of aluminum ribbon so that the plated edges may then be soldered to other materials, such as copper tubes of heat transfer coils, by means of inexpensive, soft solder.

A further object of the invention resides in the use of the zinc-immersion plating process whereby an entire flat roll of aluminum ribbon may have its side edges plated by merely immersing the entire roll into a series of plating and rinsing baths to apply to the edges thereof a readily solderable metallic material.

A further object of the invention is to provide a process for plating the side edges of a roll of aluminum ribbon material in which the entire roll is zinc coated by 'immersion in a dilute solution of zinc oxide and caustic soda at room temperature, followed by an electro-plating process to apply a solderable material such, for example, as copper, tin or bronze to the zinc-coated side edges of the ribbon material.

Another object of the invention is the plating of aluminum ribbon material of double width for use where it is only necessary to have a solderable substance applied to one edge surface thereof, the entire roll of aluminum ribbon having its surfaces edge-plated, and the roll being subsequently split to provide twice the ribbon material of desirable width having a readily solderable substance applied to one edge only thereof.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part 0f this vspecification wherein like reference characters designate corresponding parts in the several views.

In the drawings:

FIG. l is a plan view of a coil of aluminum ribbon material, to the side edges of which it is desired to apply a readily solderable substance;

FIG. 2 is a side elevational view of the coil of FIG. l;

FIG. 3 is a diagrammatic view of the preferred plating process;

FIG. 4 is a diagrammatic view of the treatment of the aluminum coil subsequent to plating; and

FIG. 5 `is a much enlarged cross-sectional view of the ribbon material, showing the solderable material applied to the opposite side edges thereof.

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and Larrangement of parts illustrated in the accompanying drawings, since the invention is capable of other `embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

The aluminum roll which is treated according to the present invention is illustrated in FIGS. l and 2. As may be seen, the roll 10 comprises a series of tightly wound convolutions 12 of aluminum ribbon. As shown in FIG. 2, the side edges 13 of the aluminum ribbon `are substantially aligned so that only the edge portions of the ribbon are exposed. The ribbon is wound tightly so that a minimum of plating solution will seep between the layers. The roll may contain about 8500 linear feet, al-

though more or less may be used depending upon the particular equipment available for plating. The aluminum ribbon is wound around a metal drum 14 and strapped in place by straps 16. The metal drum may serve as part of the electrical contact for the electro-plating steps. The resultant disc-shaped units may be plated, several at a time, just as though they were solid pieces.

The aluminum ribbon which is wound around the drum 14 to form the discs is preferably twice the width of the desired finished material. This reduces the net plating costs considerably because it is usually only necessary to have one edge of the ribbon plated, by providing the ribbon double size, it is possible to cut it into two desired width ribbons to yield twice the production. The cutting operation does not increase the cost appreciably because it can be included in the last operation which requires that the ribbon be unwound, cleaned, dried and recoiled for storage.

The plating process, indicated diagrammatickally in FIG. 3, is the well-known zinc-immersion plating process. In this process, ya coating of zinc is first chemically applied to the aluminum as an undercoat preparatory to electro-plating other materials onto the aluminum. The zinc-immersion process is considered to be the most practical method of plating aluminum. This method is described in detail in the paper Plating on Aluminum Alloys, by Fred Keller and Walter G. Zelley of Aluminum Company of America, published in the thirty-sixth Annual Proceedings of the American Electroplaters Society.

Brieliy, the method consists of immersing a clean piece of aluminum with a uniform oxide lm thereon into a sodium zincate solution. This causes the oxide coating to dissolve, exposing the pure aluminum. The pure aluminum then replaces the zinc in the zinc salt solution and then, as this occurs, the piece of aluminum becomes covered with a very thin lm of pure Zinc. As soon as the entire surface is covered with zinc, the action virtually stops and the material may then be plated with heavier coatings of material suitable for soft soldering.

Referring more specifically to FIG. 3, the preferred process for coating the roll is illustrated in detail. The entire plating process requires twelve successive steps. Eight separate tanks are used in the process. The rst tank 18 contains an alkaline cleaner, the second tank 20 contains a water rinse, the third tank 22 contains the zinc-immersion solution, the fourth tank 24 is an acid rinse, the fifth tank 26 is a water rinse, the sixth tank 28 is an electro-plating tank for applying a copper lm, the seventh tank 30 contains a solution for bronze-electroplating, and the eighth tank 32 is a water rinse.

The aluminum roll is first dipped in tank 18 to clean and condition the aluminum surface by removal of oil, grease, dirt and other contamination. A suitable cleaner is a water solution of 3% sodium carbonate and 3% sodium phosphate. The temperature of the solution may be 14C-180 F. and the roll should remain in the solution for from one to three minutes.

Subsequent to the cleaning operation, the roll is dipped in water rinse tank 20 as indicated by arrow A. This rinse step removes the alkaline cleaner material and prevents contamination of the solutions in the remaining tanks.

After the roll has been rinsed in tank 20, it is dipped in the zinc-immersion tank 22, as indicated by arrow B. The first Zinc-immersion is not intended as the final zinc coating step, but rather is a conditioning treatment to remove the surface oxide lm present on the aluminum and further condition the surface for plating. The rst zinc coating is subsequently followed by a second zinc coating. As an alternate to this double dip in the zincimmersion solution, `a hot acid etch in a sulfuric acid solution may be used to remove the surface oxide lm and other undesirable constituents. Subsequent to the first zinc-immersion, the roll is again rinsed in tank 20 as indicated by arrow C. The roll is then dipped in tank 24 as indicated by arrow D. Tank 24 contains a nitric acid solution and removes the rst Zinc coating. After the acid rinse, the roll is rinsed in a second water rinse contained in tank 26 as indicated by arrow E.

The roll is then again immersed in the zinc-immersion tank 22 as shown by arrow F -at which time the nal zinc coating is applied.

After the second zinc-immersion treatment, the roll is again water rinsed in tank 26 as indicated by arrow G. The final zinc coating has now been applied and the readily solderable material may be electro-plated thereon. As indicated by arrow H, the roll may be conventionally electro-plated in tank 28 to coat the zinc surface film with a thin layer of copper. This step is known as a copper strike. The copper strike is not absolutely necessary but it is preferred to give a good bond for the final plating of readily solderable material. This electroplating operation takes about five minutes.

After the copper strike, the roll is again water rinsed in tank 26 as indicated by arrow I. After the rinse, the roll is electro-plated in tank 30, which contains means for bronze plating. This plating step takes about five minutes. The bronze plate is the readily solderable material referred to. After the bronze plate, the roll is water rinsed in tank 32 as indicated by arrow K. This completes the plating process.

As shown in FIG. 4, after the ribbon has been plated, it is unwound, passed through a pair of rollers 34, 36 and into a wash-and-dry station 38. Upon exiting from the wash-and-dry station, the ribbon is again passed through a pair of rollers 40, 42 at which time it is split along its longitudinal axis into two strips 44, 46. The splitting operation may simply comprise a knife-edge positioned adjacent the rollers 40, 42. A pair of rollers 48, 50 then direct the strips onto a pair of drums 52, 54 for rewinding. The resultant coils may then be stored until used.

As shown in FIG. 5, the aluminum ribbon 56, before being slit into two strips, has a coating 58, 60 on each edge thereof. This coating is readily solderable and does not require special soldering techniques to form a bond with other solderable materials.

It may be thought that the application of the readily solderable material as indicated in the proposed plating process would result in a nal roll having its convolutions stuck together by the plating material so as to prevent unwinding. However, such is not the case. The zinc coating is a very thin layer of metallic zinc. It is chemically applied and there is no bridging over from one convolu tion of the roll to the next. The subsequent copper strike and bronze-plated coating will be applied to only the zinc coating, not to the adjacent aluminum. Consequently, the subsequent plating will not bridge over. Therefore, the convolutions do not stick together and may be readily unwound at the end of the process.

The readily solderable material referred to may be such as bronze, copper, tin, or silver and the like. The readily solderable material may be applied directly to the zinc coating if desired, however, best results are obtained when a copper strike is used before application of the readily solderable material.

While the aluminum strip having only one side edge soldered has been indicated as having particular use in connection with heat transfer applications, it will be appreciated that the invention is capable of use in other fields, for example in the electrical art. There are many instances in electrical applications where it is desired to solder aluminum to some other material and for such usage the present invention has value.

Having thus described our invention, we claim:

1. A method of rendering the side edge portions of aluminum ribbon material solderable comprising, providing the ribbon material in a spirally wound roll having a plurality of convolutions; said roll having side surfaces formed by the side edge porions of the ribbon; applying a coating of zinc over the entire side surfaces of said roll; and thereafter applying a coating of readily solderable metallic material over the zinc coating on said roll; whereby when said roll is unwound only the side edges will be coated with the readily solderable metallic material.

2. The method of claim 1 and further characterized in that the Zinc coating is applied by immersing the entire roll in a zinc-immersion bath.

3. The method of claim 1 and further characterized in that the readily solderable metallic material is applied by electro-plating.

4. The method of claim 1 and further characterized in that a copper coating is electro-plated between the Zinc coating and the readily solderable metallic coating.

5. The method of claim 1 and further characterized in that the readily solderable material is bronze.

6. A method of rendering the side edge portions of aluminum ribbon material solderable comprising, providing the ribbon material as a spirally wound roll having a plurality of tightly wound convolutions; said roll having side surfaces formed by the side edge portions of the ribbon; cleaning the outer surface of said roll of contaminants; applying a rst coating of zinc on the entire side surfaces thereof by immersing the entire roll in a zinc-immersion bath; removing said first zinc coating by means of an acid; applying a second zinc coating over the entire side surfaces thereof by again immersing the roll in a Zinc-immersion bath; electro-plating a thin layer of copper over said second zinc coating; and then electroplating a layer of readily solderable metallic material over said copper layer, whereby when said roll is unwound only the side edges will be coated with the readily solderable metallic material.

7. The method of producing an aluminum ribbon material having one side edge portion thereof solderable comprising, providing the ribbon material in a spirally wound roll having a plurality of tightly wound convolutions; said roll having side surfaces formed by the side edge portions of the ribbon; electro-plating a readily solderable metallic material onto the side surface of the roll to thereby provide said metallic material on the side edge portions of the ribbon; then unrolling the ribbon from the roll and splitting the ribbon longitudinally to form a pair of ribbons of material each of which has a readily solderable metallic material coated on only one side edge thereof.

8. The method of rendering the side edge portions of aluminum ribbon material solderable comprising, providing the ribbon material in a spirally wound roll having a plurality of tightly wound convolutions; said roll having side surfaces formed -by the side edge portions of the ribbon; and then electro-plating a readily solderable metallic material over the entire side surfaces of the roll by immersion of the roll into a series of electro-plating baths; whereby when said roll is unwound only the side edges of the ribbon material will be coated with the readily solderable metallic material.

References Cited in the le of this patent UNITED STATES PATENTS 2,436,227 Phillips Feb. 17, 1948 2,668,936 Robinson Feb. 9, 1954 2,887,766 Fike et al May 26, 1959 2,891,309 Fenster June 23, 1959 

1. A METHOD OF RENDERING THE SIDE EDGE PORTIONS OF ALUMINUM DRIBBON MATERIAL SOLDERABLE COMPRISING, PRO-I VIDING THE RIBBON MATERIAL IN A SPIRALLY WOUND ROLL HAVING A PLURALITY OF CONVOLUTIONS; SAID ROLL HAVING SIDE SUFACES FORMED BY THE SIDE EDGE PORTIONS OFTHE RIBBON; APPLYING A COATING OF ZINC OVER THE ENTIRE SIDE SURFACES OF SAID ROLL; AND THEREAFTER APPLYING A COATING OF READILY SOLDERABLE METALLIC MATERIAL OVER THE ZINC COATING ON SAID ROLL; WHEREBY WHEN SAID ROLL IS UNWOUND ONLY THE SIDE EDGESS WILL BE COATED WITH THE READILY SOLDERABLE METALLIC MATERIAL. 